Professor John D. Clemens, M.D.
Director, International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b)
Professor John D. Clemens, M.D. and Professor Jan R. Holmgren, M.D., Ph.D. worked jointly for over 30 years to study and develop oral cholera vaccine (OCV).
Cholera is a gastrointestinal disease due to bacterial infection. The worldwide spread, or pandemic, occurred for the first time in the 19th century, and there have been 7 pandemics till now. Millions of people have died from cholera. Injectable vaccines have been used to prevent cholera for a long period despite low efficacy. During the 1970s, Prof. Holmgren demonstrated that an important immunity against cholera is IgA produced on the mucosal surface of intestines. Thus, oral vaccines would be more efficient in inducing protection than injectable vaccines. Prof. Clemens played an important role to clinically prove the efficacy of OCV. As a result, WHO has recommended that cholera vaccines should be given orally and discontinued the use of injectable vaccines.
The first OCV was called Dukoral. However, it was expensive and difficult to administer with a protection efficacy of only 50% and only lasted 2 years. During the 2000s, Prof. Clemens and Prof. Holmgren produced a new OCV known as Shanchol. This new vaccine was cheap and provided a protection of up to 5 years. In addition, they demonstrated the concept of “herd immunity” by which providing vaccinations to at least 60% of the population can prevent on outbreak. This is because the vaccinated population can reduce incidences of disease so that the unvaccinated population would have much less of a chance of contracting the disease. Therefore, diseases can be controlled even not all of population are vaccinated. With this concept, WHO has recommended Shanchol vaccine for countries struggling to control cholera since 2010. In 2013, WHO and GAVI established an OCV stockpile to prevent a spread of cholera especially when there is a threat or a disaster-level situation. For example,
the use of OCV among several hundreds of thousands of people in Haiti after hit by Hurricane Matthew in 2016 and in Bangladesh after a heavy influx of Rohingya following the migration crisis in 2017 was believed to have helped prevent an epidemic of cholera.
A significant discovery from basic research and clinical test regarding vaccines against cholera has been approved by WHO. Prof. John D. Clemens and Prof. Jan R. Holmgren have made a great impact by recommending that cholera vaccines, be provided orally rather than injected. This also led to the establishment of an OCV stockpile to support countries at risk of or affected by the spread of cholera to help save the lives of millions of people worldwide.